This invention relates to a bleed valve of a compressor, in particular a compressor of a bypass aero-engine, with a guiding device provided downstream of a valve body in the bleed duct, said guiding device directing the bleed airflow from a compressor duct into a bypass duct in such a manner that the direction of flow of the bleed airflow is imparted a component which is unidirectional with the airflow carried in the bypass duct. For background art, reference is made to Specification U.S. Pat. No. 4,463,552, by way of example.
It is generally known that compressors, in particular those for gases, are provided with bleed valves to preclude the compressor from exceeding its surge limits, i.e. some of the gas flow or airflow compressed in the compressor is bled, if necessary, from the compressor without passing all stages of the multi-stage and in particular the multi-stage axial-flow compressor. In the case of bypass aero-engines, the so-called bleed airflow of the compressor is introduced into the bypass duct which carries the airflow supplied by the engine fan.
The known, simple bleed valves are provided with discharge ducts which introduce the bleed airflow into the bypass duct essentially vertically to the bypass airflow carried therein. In these designs, the outlet ports of these discharge ducts are vertical to the wall of the bypass duct. Since the bleed airflow can be very hot, failure of the bleed valve or its control is liable to cause damage to the bypass duct or its wall, respectively, in particular if the bleed valve is open for a longer period of time. The hot supersonic flow bled from the compressor will then have a detrimental effect on the structure of the bypass duct and the components adjacent to it.
The bleed valve taught in Specification U.S. Pat. No. 4,463,552 mentioned in the beginning reduces this detrimental effect by way of a guiding device which introduces the bleed airflow to the bypass duct in at least partly the direction of flow of the airflow carried therein; however, in a broad aspect, the present invention provides further, beneficial features to remedy the above problematics.
It is a particular object of this invention to provide a so-called dissipation screen in the bleed duct between the valve body and the guiding device. Further aspects and advantages of the present invention are cited in the subclaims.
Besides the guiding device, the present invention provides a dissipation screen which reduces some of the kinetic energy, i.e. some of the impulse of the bleed airflow. Upon being released via the opened valve body, the bleed airflow passes this essentially narrow-meshed dissipation screen (or dissipation grid or the like) provided in the bleed duct of the bleed valve and, via the guiding device, enters the bypass duct in the desired direction of flow. The swirling and intensive throttling action at the so-called dissipation screen reduces the impulse of the bleed airflow introduced to the bypass duct to such an extent that it will produce virtually no detrimental effect on the bypass duct. In addition, the dilution between the airflow carried in the bypass duct and the bleed airflow introduced to it will thus be improved, a generally desirable effect.
With regard to the operation of the guiding device, the provision of a so-called attenuation chamber between the guiding device and the dissipation grid can be beneficial to partly reduce the swirl effected at the dissipation screen (or grid). A guiding device which is particularly favorable since it includes the function of a screen (or grid) is explained in claim 3, according to which the guiding device is designed as a plate which is essentially parallel to the wall of the bypass duct, this plate being provided with a plurality of bores whose axes are inclined in the direction of flow of the airflow carried in the bypass duct. Here, optimum results are obtained when the surface of the guiding device is essentially twice the surface of the dissipation screen since, then, the additional throttling effect at the dissipation screen will not impair the throughput potential of the bleed valve.
Further objects and advantages of this invention will become apparent from the following detailed description of a preferred embodiment read in the light of the accompanying FIG. 1 which illustrates a cross-section of a compressor bleed valve in accordance with the present invention in the installed state (between a compressor annulus and a bypass duct), with reference being made to FIG. 2 which shows the View X of FIG. 1. In this context, all features described in detail can be essential for the invention.